1. Field of the Invention
The present invention relates to an inductance element used in general electronic devices or industrial electronic devices.
2. Description of the Related Art
FIG. 11 is a view showing an example constitution of a conventional inductance element. As shown in the view, an inductance element 1 is composed of a ring core 2, a drum core 6, and a coil 7.
The ring core 2 here is composed of a cylindrical magnetic member having a through hole 3 inside thereof. On upper portions of the ring core 2, connecting terminals 4, 5 with which tips of the coil 7 is to be connected are provided. Inside the through hole 3, the drum core 6 is disposed.
The drum core 6 is composed of an upper flange section 6a, a body section 6b, and a lower flange section 6c. The coil 7 is wound around the body section 6b. 
In such an inductance element 1, favorable magnetic saturation characteristic is obtainable by leaking parts of magnetic flux outward through a gap G1 between the upper flange section 6a of the drum core 6 and the ring core 2 as well as a gap G2 between the lower flange section 6c of the drum core 6 and the ring core 2. However, if the gaps G1, G2 are excessively large, an absolute value of initial inductance lowers. Hence, it is required to place these gaps G1, G2 under a control and whether or not the gaps are assembled in compliance with design values has to be controlled accurately so that the inductance element 1 has an optimal inductance element value and a rated current value.
Therefore, for obtaining the gaps G1, G2 adequately, there are disclosed techniques as shown in Japanese Patent Application Laid-Open No. 2002-313635 (abstract, claims) (Patent document 1) and Japanese Patent Application Laid-Open No. Hei 11-54333 (abstract, claims) (Patent document 2).
The technique disclosed in Patent document 1 provides a projection on either an circumferential edge portion of an upper surface of a lower flange section or a bottom end surface of a ring core so that the projection comes into contact with the other surface to form a gap.
Meanwhile, the technique disclosed in Patent document 2 is composed of a square drum core having a base board with a step portion to fit with a case core and a flange at the other end to fit with the case core, and a square case core covering over the drum core such that a gap is provided between the step portion and the flange, in which small protruding parts serving as spacers are provided on the step portion and four outer side surfaces both of the flange, respectively, or otherwise on the step portion and four inner side surfaces facing the flange both of the case core, respectively.
Meanwhile, as a ring core and drum core, such a ferrite sintered compact with high magnetic permeability that is obtained by performing powder molding and then burning a metal oxide is used. Burning a ferrite causes shrinking of a member, so that a size control becomes difficult. On the back of this, in the technique disclosed in Patent documents 1, 2, the size control of the protruding part is difficult, therefore there are sometimes cases where a setting of a gap is not appropriate, or where a protruding part does not fit with a recession suitably in the worst case.